Luminescent, Freestanding Composite Films of Au15 for Specific Metal Ion Sensing

A highly luminescent freestanding film composed of the quantum cluster, Au-15, was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu2+ has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg2+, As3+ and As5+. The composite film exhibited visual sensitivity to Cu2+ up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu2+ sensing may be due to the reduction of Cu2+ to Cu1+/Cu-0 by the glutathione ligand or the Au-15 core. Extended stability of the luminescence of the film makes it useful for practical applications.